The embryoinic development of the nervous system involves the generation of enormous cell diversity and precise cellular pattern. In some nervous systems, the cellular specificity is such that individual neurons can be uniquely identified on the basis of their characteristic shape, properties, and interactions. We would like to understand how individual nerve cells know who they are (cell determination) and where they should go (pathway selection by migrating cells and growth cones). Answering these questions will involve understanding at a cellular and molecular level the contributions of mitotic ancestry and cell interactions to each cell's unique determination and choice of pathway(s). At present there is relatively little information on the cell interactions and cell-specific molecules involved in the determination and guidance of individual neurons during embryogenesis. The grasshopper embryo is an extremely favorable prepararion in which to study cell determination and interactions of individually identified neurons; the embryonic nervous system is relatively simple, highly accessible, and well described. In an effort to reveal cell-specific molecules involved in neuronal development, we have quite successfully begun to make monoclonal antibodies against grasshopper neurons, and polyclonal antibodies against known molecules. For example, one monoclonal antibody, I-5, specifically recognizes particular identified embryonic neurons just after their final cell division and reveals patterns of cell-specific determinants between daughter cells. This proposal is to study cell determination and interactions of embryonic neurons (i) by using the monoclonal antibody technique to reveal cell-specific molecules of potential developmental importance, (ii) by localizing and characterizing the molecules, (iii) by using mono- and polyclonal antibodies to localize known molecules early in development, and (iv) by using these mono- and polyclonal antibodies as cell determination markers and potential cell interaction markers in conjunction with other cellular techniques in embryo culture. Thus, we hope to produce an array of cell-specific antibody markers to early embryonic neurons, and to use these antibodies with a variety of other techniques to better understand neuronal development.